Structure and dynamics of the Pacific North Equatorial Subsurface Current

Area of Science:

• Oceanography
• Physical Oceanography
• Climate Science

Background:

• The North Equatorial Subsurface Current (NESC) is a recently identified westward flow beneath the North Equatorial Countercurrent in the Pacific.
• Understanding its structure, properties, and dynamics is crucial for comprehending Pacific Ocean circulation.

Purpose of the Study:

• To investigate the structure, water mass properties, and dynamics of the NESC.
• To validate NESC geostrophic currents with direct measurements.
• To explore the driving mechanisms and variability of the NESC.

Main Methods:

• Analysis of Argo profiles and geostrophic currents.
• Validation using moored current meter observations in the western tropical Pacific.
• Numerical simulation using a linear continuously stratified ocean circulation model.

Main Results:

• The NESC exhibits mean westward geostrophic currents validated by direct measurements.
• Significant seasonal and interannual variability was observed, with stronger transport during boreal summer and La Niña, and weaker transport during boreal winter and El Niño.
• NESC water masses are a mix of North and South Pacific intermediate waters.
• Model simulations indicate wind curl as the forcing mechanism for the mean NESC via low baroclinic mode responses.

Conclusions:

• The NESC is a significant westward subsurface current in the Pacific Ocean.
• Its transport is strongly influenced by seasonal cycles and ENSO events.
• Ocean circulation models suggest wind curl is a primary driver of the NESC.